Manually driven transfer pump for liquefied gases

ABSTRACT

This invention is a manually driven pump used to transfer a liquefied gas such as nitrous oxide or carbon dioxide between containers. The pump is designed to minimize friction, can be directly attached to a mother bottle, and has an automatic piston return on the pumping stroke, all of which optimize operator use for the particular gas which is being pumped. The pump is small, portable, and requires no additional power source in its operation, making it ideal for field use. The pump can be used to fill nursing bottles from a mother bottle or to raise the pressure of a nursing bottle to a desired operating level.

This invention is a manually driven pump used to transfer nitrous oxide,carbon dioxide, or other liquefied gas between storage containers,requiring no other energy source such as electricity or compressed airfor its operation. It is small and easily portable, making it ideal forfield use for nitrous oxide snowmobile applications or carbon dioxidepaintball applications. It can also be used to raise the pressure of aliquefied gas container to a desired level.

BACKGROUND

Description of Prior Art

Nitrous oxide, sometimes just called nitrous, is an oxidizing agent andwhen delivered to an engine, results in an increase in engine poweroutput. The nitrous is pressurized and stored in a container as a liquidin equilibrium with its vapor, thereby allowing a relatively high massstorage density. Since the liquid is in equilibrium with its vapor, thepressure of the nitrous in the bottle is determined by its temperature.For instance, at 0 degrees Celsius, the bottle pressure is 31 E06dynes/cm̂2 (450 pounds per square inch (PSI)); when at 22 degreesCelsius, the bottle pressure is 51E06 dynes/cm̂2 (735 PSI). Carbondioxide pressure is similar; zero degree Celsius pressure is 36E06dynes/cm̂2 (520 PSI) and 22 degrees Celsius pressure is 61E06 dynes/cm̂2(880 PSI). Liquefied nitrous oxide and carbon dioxide have very similarthermodynamic characteristics and transfer pumps presently manufacturedcan be adapted to pump either nitrous oxide or carbon dioxide.

Nitrous oxide delivery systems used for engine power enhancementtypically contain a relatively small nitrous bottle, commonly called a“nursing bottle”, to store a relatively small amount of nitrous on thevehicle, but use a larger bottle, commonly called a “mother bottle”, tostore larger amounts of nitrous oxide apart from the vehicle. Motherbottles typically hold between 9000 grams (20 pounds) of nitrous andlarger ones hold 30,000 grams (65 pounds). Nursing bottles holdconsiderably less; 1100 grams (2.5 pounds) is typical for a snowmobilewhich has a nitrous system installed to increase horsepower for dragracing or mountain climbing. This amount of nitrous only lasts arelatively short time; typically 1100 grams of nitrous is used in 30 to100 seconds of nitrous system operation.

Presently, two methods are commonly used to replace the nitrous on thevehicle in the field. One method is to have more than one nursingbottle, perhaps two to four, these bottles having previously been filledat a refill station. These are replaced on the vehicle as required. Thisis relatively expensive because of the purchase of the extra bottles.Also, this puts a practical limit on the amount of nitrous which can bestored at the race site or on the side of a mountain. For instance, ifthe snowmobile operator has four nursing bottles at 1100 grams each,this only provides 4400 grams total on site, which is less than halfwhat one 9000 gram mother bottle and one 1100 gram nursing bottle holds,and is considerably less than what is contained in a 30,000 gram motherbottle.

The other method is to have a current technology refill station on site.These refill stations use a transfer pump which is relatively expensive,large, heavy, and typically requires a source of compressed air in itsoperation. These refill stations are difficult to use at a race site oron a mountain because of the above limitations.

Compressed carbon dioxide is used in the game of paintball. Paintballguns are driven by compressed carbon dioxide which is held in arelatively small nursing bottle which, as in the case of nitrous, mustbe filled from a mother bottle. Similar problems with field filling arealso encountered in this industry.

In addition, there are instances where the pressure in a nursing bottlemust be kept at a certain level. Applicant holds U.S. Pat. No. 6,938,841which is a nitrous oxide jet which varies in size according to bottlepressure to maintain a constant nitrous flow rate. Other manufacturersof nitrous systems, however, not having this technology, for propersystem operation require the users of their systems to maintain acertain nitrous bottle pressure, 62E06 dynes/cm̂2 (900 PSI) for instance.Presently, users of these systems maintain this bottle pressure byheating, either using bottle heaters or illegally using a torch appliedto the bottle.

OBJECTS AND ADVANTAGES

It is an object of this invention to provide a manually driven pump forthe transfer of liquid nitrous oxide, liquid carbon dioxide, or otherliquefied gas which requires no other energy source for its operation.

It is a further object of this invention to provide a manually drivenpump for the transfer of liquid nitrous oxide, liquid carbon dioxide, orother liquefied gas which is relatively small, has relatively lowweight, and is relatively inexpensive to produce.

It is a further object of this invention to provide a manually drivenpump for transfer of liquid nitrous oxide, carbon dioxide, or otherliquefied gas which can easily be attached directly to a mother bottlewhich is delivering the nitrous oxide, carbon dioxide, or otherliquefied gas.

It is a further object of this invention to provide a manually drivenpump for transfer of liquid nitrous oxide, carbon dioxide, or otherliquefied gas which is specifically designed for efficient operationwith the pressure characteristics of the liquefied gas with which itwill be used.

It is a further object of this invention to provide a manually drivenpump for transfer of liquid nitrous oxide, carbon dioxide, or otherliquefied gas which can be used to raise the pressure of a liquefied gascontainer to a desired operating level.

Still further objects and advantages will become apparent from aconsideration of the ensuing description and drawings.

DRAWING FIGURES

FIG. 1 shows in cross-section a manually driven pump which can transfernitrous oxide or other liquefied gas.

FIG. 2 shows in partial cross section the manually driven pump of FIG. 1with its inlet directly attached to a mother bottle containing nitrousoxide, carbon dioxide, or other liquefied gas and its outlet connectedto a nursing bottle through a conduit.

REFERENCE NUMERALS IN DRAWINGS

-   1 manually driven transfer pump assembly-   10 pump body-   12 threaded body inlet-   14 inlet sealing washer-   20 threaded body outlet-   30 bore-   31 bore inlet chamber-   32 bore pump chamber-   40 outlet connection and one-way valve assembly-   42 outlet body-   46 threaded flare connection-   50 one-way valve sealing ball-   51 one-way valve seat-   52 one-way valve spring-   60 bushing-   61 bushing retaining ring-   62 bushing bore o-ring-   64 bushing rod o-ring-   70 rod and piston assembly-   72 rod-   74 knob-   76 piston-   78 piston o-ring-   80 wave washer-   82 rod retaining ring-   100 mother bottle assembly-   102 mother bottle-   104 material in liquid state-   106 material in vapor state-   110 mother bottle valve assembly-   111 mother bottle valve body-   114 mother bottle valve connection threads-   116 mother bottle valve knob-   117 mother bottle valve stem-   118 mother bottle valve seat-   119 mother bottle siphon tube-   120 bottle nut-   122 bottle nut threaded flare connection-   150 nursing bottle-   152 nursing bottle threaded flare connection-   160 connection conduit

Description and Operation—FIGS. 1 and 2

FIG. 1 shows a preferred embodiment of a manually driven transfer pumpassembly 1 which can transfer liquefied gases such as nitrous oxide andcarbon dioxide from one storage bottle to another. Pump assembly 1contains a body 10 (preferably aluminum) with three openings; a threadedinlet 12 with sealing washer 14, a threaded outlet 20, and a bore 30. Anoutlet connection and one-way valve assembly 40 is threadably engaged inoutlet 20 and contains an outlet body 42 with threaded flare connection46. The one-way valve function of assembly 40 is provided by a sealingball 50 which is urged toward a seat 51 by a pre-loaded spring 52. Abushing 60 (preferably bronze) is held in a counterbore of bore 30against pressurization of bore 30 by a bushing retaining ring 61.Bushing 60 seals to bore 30 using a bore o-ring 62 and to a rod 72(preferably stainless steel) of a rod and piston assembly 70 using a rodo-ring 64. In addition to rod 72, rod and piston assembly 70 contains aknob 74 used for manual force application, a piston 76 with a pistono-ring 78 movably held near piston 76 by a rod retaining ring 82 and awave washer 80. Piston o-ring 78 divides bore 30 into a bore inletchamber 31 and a bore pump chamber 32.

FIG. 2 shows pump assembly 1 threadably sealed/attached to a motherbottle assembly 100. Assembly 100 contains a bottle 102 which contains aliquefied gas in equilibrium with its vapor, the liquid portion shown as104 and the vapor portion as 106. Mother bottle assembly 100 alsocontains a valve assembly 110 containing a valve body 111 withconnection threads 114. Valve 110 also contains an operating knob 116connected to a sealing stem 117 which can seal against a seat 118. Valve110 is connected to liquid portion 104 of the liquefied gas using asiphon tube 119. If mother bottle 100 does not contain siphon tube 119,then it should be inverted. Each material contained in mother bottle 100has a unique valve connection thread 114 determined by the CompressedGas Association to prevent placing the wrong material in mother bottle100, and a bottle nut 120 is normally used to convert the particularthreads 114 of mother bottle valve 110 to a common threaded flareconnection 122. Transfer pump assembly 1 is shown threadably attachedand sealed to bottle nut 120; the threads of flare connection 122 ofbottle nut 120 match the threads of inlet 12 of pump assembly 1 andwasher 14 is designed to seal to the flare portion of connection 122thereby eliminating the need for tightening with a wrench. A nursingbottle 150, normally considerably smaller in capacity than mother bottle100, is shown connected to the outlet connection 40 of pump assembly 1using a conduit 160 which has appropriate female flare fittings to sealto outlet 40 of pump 1 and a threaded flare fitting 152 of nursingbottle 150.

The filling procedure for an empty nursing bottle 150 is as follows.Inlet 12 of pump assembly 1 is connected to mother 100 bottle containinga liquefied gas such as nitrous oxide or carbon dioxide and its outlet40 is connected to nursing bottle 150 which normally contains air atatmospheric pressure. Mother bottle valve 110 is opened first and thenthe valve of nursing bottle 150 is opened. Mother bottle 100, since itcontains a liquefied gas, has a pressure which is high relative toatmospheric. This high pressure is easily able to overcome the “pop-off”or opening pressure of the one-way valve in outlet fitting 40 of pumpassembly 1 since the pre-load of spring 52 urging ball 50 toward seat 51is normally set to give a relatively low pop-off pressure, typically350,000 dynes/cm̂2 (5 PSI) or less. The effect of pop-off pressure onassembly 1 operation will be ignored in subsequent discussion since itis normally relatively small but can easily be included in anycalculations if it is significant for a particular design. Liquefied gasflows from mother bottle 100 to nursing bottle 150 until the pressure inthe two bottles is essentially equal (modified slightly by the pop-offpressure of one-way outlet fitting 40) at which point the one-way valveof outlet fitting 40 closes.

Pressurization of pump assembly 1 initially forces rod 72 to its fullyextended position out from bushing 60 with a consequent minimum volumein pump chamber 32 and a maximum volume in inlet chamber 31. An operatorof pump 1 then applies a sufficient inward force to knob 74 andconsequently rod 72 to overcome the outward force on rod 72 due to thepressurization of assembly 1 and any frictional forces present. Rod 72and piston 76 move to the left, decreasing the volume of bore inletchamber 31 and increasing the volume of bore pump chamber 32. Pistono-ring 78 has an internal diameter larger than the outside diameter ofrod 72 but an outside diameter larger than the diameter of bore 30, anddue to its inherent rigidity and consequent friction against bore 30, itmoves away from piston 76 and against wave washer 80. O-ring 78 cannotseal in this position due to the waves in washer 80, and thereforeliquefied gas moves freely past o-ring 78 from bore inlet chamber 31into bore pump chamber 32. This stroke wherein pump chamber 32 is filledis called the filling stroke of pump assembly 1.

When the operator has forced rod 72 to its fully inserted position, theinward force is removed and rod 72 will again move outward due to thepressure on rod 72. The pressure in bore pump chamber 32 will riseslightly above the pressure in bore inlet chamber 31 due to the pop-offpressure of the one-way valve contained in outlet fitting 40. This,combined with the rightward movement of piston 76 and the o-ring 78frictional effects discussed above, moves o-ring 78 away from wavewasher 80 and against piston 76 where it consequently seals piston 76 tobore 30. This rightward movement decreases the volume of bore pumpchamber 32, thereby increasing its pressure and opening the one-wayvalve in outlet 40, and liquefied gas exits pump 1 toward nursing bottle150. When rod 72 is fully extended and becomes stationary, the pressureacross ball 50 ceases since there is no further movement of fluidthrough seat 51. Ball 50 moves against seat 51 thereby trapping upstreama portion of the liquefied gas which has passed through seat 51. This iscalled the pumping stroke. Pumping and filling strokes are repeated andthis is the pumping action of assembly 1.

Nursing bottle 150 is not always empty when the filling process beginsas described above but can be partially full. In this case the pumpingaction is similar to that above except for the initial flow from motherbottle 100 to nursing bottle 150. As above, downstream flow through pumpassembly 1 will occur if the pressure in nursing bottle 150 happens tobe sufficiently less than the pressure in mother bottle 100 to open theone-way valve in outlet 40, for instance if nursing bottle 150 issufficiently lower than that of mother bottle 100. This flow, as above,will continue until the two bottle pressures are essentially equal. Ifthe two bottles are at the same temperature and consequently at the samepressure, no initial flow will occur. If mother bottle 100 is colderthan nursing bottle 150, a back-pressure will exist across pump 1, butone-way valve outlet connection 40 will prevent reverse flow. Subsequentpumping action is then the same as discussed above for an initiallyempty nursing bottle 150.

As pumping moves material from mother bottle 100 to nursing bottle 150,the pressure in mother bottle 100 decreases and the pressure in nursingbottle 150 increases. The decrease in mother bottle 100 pressure isnormally relatively small due to its larger size, but the increase innursing bottle 150 pressure can be substantial. For instance,transferring 454 grams (1 pound) from a 23000 gram (50 pound) capacitymother bottle 100 which contains carbon dioxide at room temperature (22degrees Celsius) results in only a slight decrease in its initialpressure of 61E06 dynes/cm̂2 (880 PSI). However, transferring 454 grams(1 pound) of carbon dioxide to a nursing bottle 150 with an 100 gram(2.5 pound) capacity initially containing 680 grams (1.5 pounds) at roomtemperature will raise its pressure by about 6.9E06 dynes/cm̂2 (100 PSI)to 68E06 dynes/cm̂2 (980 PSI).

Pump assembly 1 works best when rod and piston assembly 70 automaticallyextends outward from bushing 60 because an operator of assembly 1 is notrequired to pull assembly 70 out. Ignoring frictional effects, thisautomatic extension will occur if there is a net outward force (theoutward force less the inward force) on rod and piston assembly 70. Theoutward force is the pressure in bore inlet chamber 31 times its areawhich equals the area of bore 30. The inlet force is the pressure inbore pump chamber 32 times its area which is the area of bore 30 lessthe area of rod 72. Parameters affecting the automatic extension of rodand piston assembly 70 are the pressure characteristics of the specificliquefied gas which is being pumped, the relationship between the areasof inlet chamber 30 and pump chamber 32, and frictional forces. Pumpassembly 1 can have what's called a “pressure rating” which is themaximum outlet pressure at which rod and piston assembly 70automatically extends from pump assembly 1 for a given inlet pressure.The inlet pressure of pump assembly 1 used in establishing its pressurerating would normally be chosen to be the room temperature pressure ofthe specific liquefied gas for which it is designed, which is 51E06dynes/cm̂2 (735 PSI) for nitrous and 61E06 dynes/cm̂2 (880 PSI) for carbondioxide.

Ignoring frictional effects, the relationship between the areas of rod72 and bore 30 determines the pressure rating of pump assembly 1 for anygiven mother bottle 100 liquefied gas and temperature. For instance, ifpump assembly 1 has a bore 30 diameter of 9.5 mm (0.375 inches) and arod 72 diameter of 4 mm (0.156 inches) and it is being used with a roomtemperature mother bottle 100 containing carbon dioxide at 61E06dynes/cm̂2 (880 PSI), the pressure rating of the pump is determined asfollows. The outward force on rod and piston assembly 70 is the area ofbore inlet chamber 31 times its pressure, this pressure being the motherbottle 100 pressure since this chamber is directly connected to motherbottle 100. This outward force is 43.2E06 dynes. The inward force is thepressure in bore pump chamber 32 (essentially equal to the pressure innursing bottle 150) times its area, which is the area of bore 30 reducedby the area of rod 72. The pressure in bore pump chamber 32 at which theinward force equals the outward force can be calculated and is 73E06dynes/cm̂2 (1060 PSI). Therefore, for this application, the pressurerating of pump assembly 1 is 73E06 dynes/cm̂2 (1060 PSI) at a motherbottle pressure of 61E06 dynes/cm̂2 (880 PSI).

Another design consideration is the diameter of rod 72 and the forcerequired to push rod 72 inward. The pressure rating of assembly 1 isestablished by the pumping stroke where the pressure in bore inletchamber 31 is the mother bottle 100 pressure and the pressure in borepumping chamber 32 essentially equals nursing bottle 150 pressure. Buton the inward movement of rod 72 on the filling stroke, the pressures inchambers 31 and 32 are essentially equal due to the fact that pistono-ring 78 is not sealed, and these pressures are essentially equal tomother bottle 100 pressure. The outward force on rod 72 is stilldetermined as above using the inward and outward force calculations, butin this case since the pressures in chambers 31 and 32 are the same, theformula can be simplified. In the case of the filling stroke, theformula for the outward force on rod 72 can be simplified to be just thearea of rod 72 times mother bottle 100 pressure. This puts a practicallimit on the diameter of rod 72 which will allow relatively easyoperator function when on the filling stroke. For the same designdiscussed above with a mother bottle 100 pressure of 61E06 dynes/cm̂2(880 PSI) and rod 72 diameter of 4 mm (0.156 inches), this gives anoutward force on rod 72 on the filling stroke of 7.5E06 dynes (17pounds) which is a reasonable force for an operator of pump assembly 1to apply. Of course the diameter of rod 72 can be chosen as required toprovide optimum performance of pump assembly 1 for any combination ofliquefied gas and mother bottle 100 temperature, along with acorresponding adjustment if necessary to bore 30 diameter to achieve thedesired pump pressure rating.

Frictional effects should be minimized in pump assembly 1 to reduce theoperator's pumping effort and to maximize the pressure rating for anygiven condition. The largest sources of friction in assembly 1 arepiston o-ring 78 and bushing rod o-ring 64. A good material for both isa 90 Shore A durometer polyurethane since this material provides lowfriction, high tensile strength, and good resistance to abrasion.Normally O-rings used as reciprocating seals to seal a piston in a boreuse radial compression to provide the seal. In other words, the radialclearance between the surface upon which the o-ring is mounted and thebore is less than the cross-sectional dimension of the o-ring, hence theradial compression. In the case of a relatively hard o-ring materialsuch as this 90 durometer polyurethane material, the compressive forceon the o-ring, even for relatively small radial compression, can beconsiderable. This, coupled with additional compression of the o-ringdue to any pressure existing across the o-ring, can create relativelyhigh frictional forces in this conventional o-ring construction.

In assembly 1, however, the radial clearance between rod 72 and bore 30is greater than the cross-section of o-ring 78. This allows, asdiscussed above, o-ring 78 to move relative to rod 72 so it can performits one-way valve function, but this construction also providesinherently low friction as compared to a construction in which there isradial compression of the o-ring. In fact, when rod and piston assembly70 is moving to the left on the filling stroke and o-ring 78 is pushedagainst wave washer 80 with consequently no pressure across it, o-ring78 causes essentially no friction force on this stroke. Even when rodand piston assembly 70 is moving to the right on the pumping stroke witho-ring 78 sealing bore 30 to piston 76, the frictional force of o-ring78 is higher than on the filling stroke due to the pressure existingacross o-ring 78 but this force is still considerably less than thatwhich would be present with a conventional radially compressed o-ringconstruction.

Pump 1 has a maximum mass transfer per cycle determined by the densityof the particular liquefied gas at its temperature multiplied by themaximum volume change in bore pump chamber 32. The maximum volume changeof bore pump chamber 32 equals the area of bore pump chamber 32 (thearea of bore 30 less the area of rod 72) times the maximum stroke ofpiston o-ring 78. The actual mass transfer per cycle of pump 1 equalsthe maximum mass transfer per cycle times the pumping efficiency factorof pump 1. A pump was assembled similar to pump 1 having a bore 30diameter of 9.5 mm (0.375 inches), a rod 72 diameter of 4 mm (0.156inches), and a maximum o-ring 78 stroke of 22 mm (0.87 inches) giving amaximum volume change in bore pump chamber 32 equal to 1.3 cm̂3. Thedensity of liquefied carbon dioxide at room temperature is approximately0.77 grams/cm̂3 giving a maximum mass transfer per cycle of 1 gram. Thispump was tested and it actually pumped about 0.92 grams of liquid carbondioxide per cycle giving a pumping efficiency factor of 0.92.

An operator of pump 1 needs a scale to weigh nursing bottle 150, andknowing the tare weight of bottle 150 and its rated capacity ofliquefied gas, the operator knows how much material must be added tobottle 150 to fill it to any desired level. Therefore, knowing thedesired quantity of mass to transfer and knowing the mass transfer percycle of assembly 1, the operator knows approximately how many pumpstrokes are required to complete the filling. This eliminates much ofthe trial-and-error which can occur when filling nursing bottle 150using presently available pumps which use air pressure in theiroperation.

As discussed above, many conventional nitrous oxide delivery systemswhich do not have the adjustable nitrous jet discussed in Applicant'sU.S. Pat. No. 6,938,841 require a constant nitrous bottle pressure forproper operation. Presently, a typical procedure is to check nitrouspressure just before a race, and if it is low, to apply heat, typicallywith a torch, to raise the pressure to an acceptable level. Thisapplication of heat with a torch weakens the aluminum typically used inthese high pressure bottles, and this heating procedure is illegal.Users of these systems, however, being somewhat independent thinkers, doit anyway. Pump assembly 1 of this invention can replace this illegalheating method. As discussed above, transferring material into nursingbottle 150 raises its pressure (the bottle actually is heated internallydue to the enthalpy added to the liquid nitrous during the pumpingstroke), and this pressure increase is very gradual and easilycontrolled. A pressure gauge can be connected into conduit 160 (using a“tee” for instance) and pump assembly 1 can simply be operated until thedesired pressure level is reached.

Summary, Ramification, and Scope

This invention is a manually driven pump used to transfer a liquefiedgas such as nitrous oxide or carbon dioxide between containers. The pumpis designed to minimize friction, can be directly attached to a motherbottle, and has an automatic piston return on the pumping stroke, all ofwhich optimize operator use for the particular gas which is beingpumped. The pump is small, portable, and requires no additional powersource in its operation, making it ideal for field use. The pump can beused to fill nursing bottles from a mother bottle or to raise thepressure of a nursing bottle to a desired operating level.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. For instance, the assembly is shown with a one-wayvalve function present in an outlet fitting in the pump. This ispreferable in most cases, but this one way valve can also be placed inthe pump's inlet or one-way valves can be placed in both the inlet andoutlet if desired. The one-way valve shown is a spring loaded ball andseat design, but other one-way valve designs can be used, such as adiaphragm. The pump is shown as having an inlet which is directlyattached to a mother bottle, and this is preferable because in somecases the pumping action is easier with this connection, but in somesituations a different inlet connection may be beneficial, such as aflare connection commonly used with flexible conduits. It may bedesirable in some cases to rigidly fix the pump to a fixture such as atable, perhaps attaching the end opposite the operating rod to thefixture and placing its inlet on the side rather than on its axis. Itmay even be desirable in some cases to have the operating shaft extendcompletely through the pump along its axis, thereby eliminating theautomatic rod extension function present in the preferred embodimentshown. Thus, the scope of the invention should be determined by theappended claims and their legal equivalents, rather than by the examplesgiven.

1. In a pump used to transfer a liquefied gas from a first container toa second container, wherein said first container contains a liquefiedgas in equilibrium with its vapor at a first pressure level, and whereinsaid pump has a piston means, the improvement wherein said piston meansis moved by application of a manual force by an operator of said pump.2. The pump of claim 1 wherein said pump is directly attached to saidfirst container.
 3. The pump of claim 2 wherein said pump is directlyattached to said first container using an inlet fitting of said pump. 4.The pump of claim 1 wherein said second container contains a liquefiedgas in equilibrium with its vapor, and wherein said second container hasan initial second pressure and a higher desired second pressure, andwherein said pump is operated to increase the pressure of said secondcontainer.
 5. The pump of claim 1 wherein said piston means is containedin a bore of said pump, and wherein said piston means has a portionwhich passes through a sealing member, and wherein said portion has aradial clearance to said bore, and wherein said sealing means whenrelaxed has a radial thickness, the improvement wherein said radialthickness is smaller than said radial clearance.
 6. The pump of claim 5wherein said piston has a movement in a first direction and a movementin a second direction, and wherein said sealing member prevents movementof said liquefied gas past said piston means when said movement in saidfirst direction, and wherein said sealing member allows movement of saidliquefied gas past said piston means when said movement is in saidsecond direction.
 7. The pump of claim 1 wherein said liquefied gas isnitrous oxide.
 8. The pump of claim 1 wherein said liquefied gas iscarbon dioxide.
 9. The pump of claim 1 wherein internal pressurizationof said pump by said liquefied gas moves said piston means.
 10. The pumpof claim 9 wherein said piston moves in a first direction by saidinternal pressurization of said pump and in a second direction by saidapplication of said manual force.
 11. The pump of claim 9 wherein saidpump has a pumping cycle consisting of a maximum displacement of saidpiston in a first direction and a subsequent maximum displacement ofsaid piston in a second direction and wherein said maximum displacementof said piston in said first direction occurs due to said internalpressurization only.
 12. The pump of claim 1 wherein said pump has apumping cycle consisting of a maximum displacement of said piston in afirst direction and a subsequent maximum displacement of said piston ina second direction, and wherein said pump has an actual mass transferper cycle, and wherein knowledge of said actual mass transfer per cycleof said pump is used to estimate a mass which has been transferred withsaid pump.